Electric system for recording and reproducing sound



May 31, 1932. E. H. HANSEN 1,360,502

ELECTRIC SYSTEM FOR RECORDING AND REPRODUCING SOUND Filed Aug. 26, 1927 2 Sheets-Shee 1 INVENTOR. [a'mqnd Hansen.

y 1932- E. H. HANSEN 1,860,502

ELECTRIC SYSTEM FOR RECORDING AND REPRODUCING SOUND Filed Aug. 26, 1927 2 Shams-Sheet 2 INVENTOR. Edmund H. Hansen.

latented May 31, 1932 PATENT FFICE EDMUND H. HANSEN, NEW YORK, N. Y.

ELECTRIC SYSTEM FOR RECORDING AND REPRODUCING SOUND Application filed August 26, 1927. Serial No. 215,672.

This invention has reference to a system whereby sound is converted into its corresponding electrical form, and controls, or modulates a beam of polarized light, the light resultant therefrom being photographed on a light sensitive surface. A synchronizing current is converted into light variations and simultaneously recorded on the same light sensitive surface with the sound and parallel thereto.

Another object of my invention is the translation of the photographic gradations, representing sound and synchronizing vibra' tions, back into their original form.

Other objects of my invention are the d stortionless conversion of sound waves in all their complex forms into electrical modulating currents. Means are also contemplated for providing the correct light intensities for 20 linear photographic exposures in recording, together with means for a similar linear op eration of photo-electric cells in the translation of photographic gradations back into their original sound wave forms.

Another object of my invention is to devise a means whereby the speed of travel of the translation film shall be identical to that of the recording film;

Other objects of my invention are to devise certain improvements in the mechanism for carryin out the above method.

Other ob ects of my invention will be set forth in the following description, and drawings which illustrate a preferred embodiment. It being understood that the previous statements of the objects of my invention are intended merely for general explanation and not to limit my'invention in any manner whatever.

Figure 1 is a diagrammatic View of the Figure 4 is a representation of the recording film in the translation mechanism showin the relative position of this film to the lig 1t source, and attendant photo-electric and optical equipment.

Referring to the drawings, the numeral 1 indicates a source of light preferably of the concentrated incandescent type, heated from a battery source 2, and controlled for intensity by the variable resistor 3. A lens 4 con- 0 centrates light from the source 1 through a N icol. rism 5 to a focus between the electrodes of a Kerr cell 6 consisting of a glass receptaclecontaining a liquid 9.

The Nicol prism 5 in the conventional form 05 consists of two pieces of Iceland Spar cemented together. This prism is capable of plane polarization of light, and the light concentrated at a central point between the electrodes 7 should be considered as being 7 plane polarized. It has been found that when using nitro-benzol (nitro-benzene C H NO electrodes made from carbon either plated or unplated possess properties of self cleaning, and are preferred to those of ,75 brass and other metals.

The polarizer prism 5 and the analyzer prism lOare connected or attached by means of flanges in an anterior and posterior position respectively to the Kerr cell.

The sound to be recorded is first intercepted by means of a microphone preferably of the electrostatic type as indicated by the numeral 11, and placed in a circuit consisting of a resistor 12, to positive potential of battery 13, and from the negative terminal of battery 13 to the opposite plate of the electrostatic microphone 11. Sound waves impinging upon the movable plate of the microphone 11 will cause a proportionate frequency amplitude variation in the distance between the two plates of the microphone, with a resultant potential frequency variation across resistor 12, and a like 9 change on the grid 18 of a triode. A coupling condenser 16 is utilized in keeping the direct current component from reaching the grid 18. A resistor 14 is employed as a leak in preventing strong grid charges from collectin Filament 19 of the triode is heated by a attery sup ly source 20.

Anode 17 of t e triode connects to a resistor 15 and the lower electrode 7 of the Kerr cell 6. Current passes through the Kerr cell to upper electrode 7 thence to battery source 8; the negative terminal of this a source being connected to resistor 15 and positive terminal of battery 13. Resistor 15 is very high in value as compared to the circuit, battery 8 and Kerr cell 6 which it shunts, and acts in the capacity of a deolarizer. Negative terminal of batter 13 is connected to filament 19 of the trio e in the usual manner.

The complete action of the sound-electrooptical system may be said to function as follows: Sound waves varyin in amplitude and frequency are intercepted y microphone 11 and cause corresponding grid currents on grid 18, with proportionate increases or changes in currents flowing through Kerr cell 6, its electrodes 7 having similar electrostatic displacements, thus causin a like chgnge in the refractive index the liqui 9.

The polarizing rism having been previously rotated so t at light passing through it is plane polarized horizontally with respect to the surface of the electrodes 7, the effect of analyzing prism which has been placed or rotated to a point 90 degrees out of base with olarizer prism 5 is to normally cut ofi al light-reaching it with no potential on surface of the electrodes 7. Potential on the plates of the electrodes will cause a rotational shift in the plane polarized li ht passing through the Kerr cell and this phase shift up to 90 degrees will cause a correspondin increase in the light passing through t e analyzing system. Thisvarying intensity of light after passing through an optical system consisting of .condensing lenses. 22, 23 passes through a slit 25 and is recorded upon a light sensitive film 32 at a point 26.

This film, which is of standard motion picture size and character, is placed in the light tight box24, and is reeled in conventional form on the spool 27. A motor 36 has a pulle upon its shaft as well as a balance whee of the mercury type 37, also attached to this shaft being a generator 38 and its attendant collector rings 39.

The purpose of the mercury balance wheel is to impart a uniform motion to this common shaft, since any variation in speed of V pulley 35. By uti film travel will result in frequency variations of the recorded striatic structure. The sprocket 30 is rotated'bymeans of a flexible belt between the ulley 30A and the drive lizing a woven cloth belt it as been observed that a further increase in uniform drive motion is obtained.

The recording film 32 is placed upon the reel 27 threaded around a guide roller 28 through small uide rollers 29, around a sprocket 30 with the film sprocket holes engaging their relative sprocket points and finally attached to a take up reel 31. A flexible belt 34 is used to rotate the reel 31 by means of a pulley 31A and a ulley 30B.

It has been observed that where recording is desired of sound above voice fr uencies it becomes increasingly important t hat all speed variations of the recording film be ke t at a minimum, and in order to obtain t e greatest fidelity of the reproduced sound with respect to that of the original it is necessary that the speed of rotation be synchronously common to both recording, and reproducing mechanisms.

n order to accomplish this I have devised a circuit, and mechanism whereby a generator 38 is connected to the common shaft with the driving motor 36, which produces an alternating current the frequency of which varies as the speed of the motor and common shaft. In practice a generator is employed with a frequency of 500 cycles, but this may be of an desired frequency dependin upon the e ree of error in correction al owable, this r uency being generated at the normal spee ofrotation of the drivin motor 36. Current is supplied throug the collector rings 39 to the rimary of a step up transformer 40, and tom the secondary windings of this transformer to a glow am capable of following cyclic changes of t e alternator 38 with li ht discharges. This glow lamp 41 is place in optical relationship with the condensing lens 42 and the slit 43 so that light falling at a point 44 will affect the light sensitive film, and a striatic structure will result corresponding to frequency changes of the generatorx38.

By this arrangement it will be observed that whenever the recordin film 32 is being drawn from its suppl ree' 27 and passing the sound recordings it 25, it has also been exposed to light varying in fr uency proportionately with its linear spee in a given period of time, this being accom lished b means of the generator, and glow amp wit their attendant electro-optical structures.

After the usual hotographic processes have been accomplis ed consistin of developing, fixing, and washing it will be found that a photographic record similar to that 1 in Figure 2 has been obtained. The numeral 26 indicates the striatic structure formed by the sound to be recorded, while the striations at 44 have been made by the synchronizing impulses of the generator 38.

The photographic record described in the preceding paragraph is now used as a negative from which a positive print is obtained in a manner well known to the art. This is necessary due to the reversal characteristics of the recording film which if used to control the reproducing li ht would be correct in light intensity only in that portion of its density exposure characteristic curve corresponding to the Kerr cell characteristic curve. This positive record is placed within the light tight box 51 around the reel 82. This reel is free to rotateupon its shaft and the film 83 is threaded in the manner illustrated in Figure 3 so that it is guided by roller guides 84, and 85, engaged by the sprocket roller 86 and thence to the take up reel 87.

The source of motion is the motor 92 through a pulley 90 geared to the motor shaft, and thence by means of a flexible belt between the pulley 90 and the pulley 86A. The take up reel is driven from the pulley 86B by means of a flexible belt to pulley 87A attached to the shaft of the take up reel.

It is therefore apparent that any motion of the motor 92 through the intermediate gearing pulley 90 with its connecting belt 89 Will rotate pulley 86A and the sprocket 86 causing the film to be drawn from reel 82 and rewound upon the take up reel 87. Having set the speed of the motor to one whereby the linear speed of the film 83 passing the point 53 is approximately identical to that of the recording film travel the means of sound translation from this film will be explained.

A source of light which may be the filament of the incandescent type heated by a battery source 47 with its intensity controlled by the regulating resistance 46, is provided with a lens 48 which concentrates this light through a slit 49 the image of which is further reduced and intensified by means of the lenses 50 and 52, and projected through the guide slit 54 to a point on the moving film 53. This light is the image of the slit 49 and in practice is approximately .3 in width by .0005 inches in length. and is of sufficient size to cover the guide slits 54A and 54B. The guide 54 is placed in such a position that the slit 54A will be parallel and adjacent to the striatic structure 44, and slit 54B is parallel and adjacent to the striatic structure 26 both of which have been previously identified.

It is therefore to be observed that as illustrated in Figures 3, and 4, a single source of light is converged to, and divided by the two guide slits 54A, and 5413 with a further longitudinal division accomplished by the strip 55.

7 Behind the film at guide slit 54B is placed a reflector whose purpose is to reflect light from the striatic structure 26 to a point where it is intercepted by the photo-electric cell 59.

I find this method of translating sound striations on film to be a decided improvement over those wherein a beam of light passes entirely through the film structure. This is due to the granular construction of the film which produces an audible sound due to the spacing between the grain. By reflecting the guide slit 54A is interrupted by the striatic formation 44 and thence passes through the film to a point where it is intercepted by the photo-electric cell 58. The purpose of striatic formation 44 being solely that of synchronization at comparatively low frequencies no attempt is made to maintain the undistorted-levelsct for that in' reproducing the recorded sound structure 26.

Referring to Figure 3 it is seen that light reflected from striatic structure 26 to a point where it is intercepted by the photo-electric cell 59 causes an emission electronic in character internally from cathode to anode of this cell 59. Current then flows through a circuit consisting of the battery source 60, resistance 61, and the cathode, and anode of the photo-electric cell 59. The striatic interrupt-ions caused by the structure 26 to the light source 45 and its attendant optical circuit, give rise to pulsating currents varying in frequency and intensity when associated with the electrical circuit described in the precedlng sentence.

The alternating component of this current passes through the condenser 62 to the grid 64 of the triode, and from the negative side of the battery source to the filament 57 of the triode. This filament is heated by a battery source 68. The plate 55 of the triode is connected through the primary of the transformer 66 to the positive terminal of the battery source 67, the negative pole of this battery being connected to the positive terminal of the filament heating battery 68 in the coni ventional manner.

The circuit described functions in the usual relay amplifier manner, the grid 64 of the triode controlling plate current emission in accordance with intensity frequency variations of the light falling on photo-electric cell 59. A resistance 63 is provided for the proper grid voltage control.

Audio frequency currents passing through the primary of the transformer 66 set up like currents, varying solely in their potential current characteristics, in the secondary winding, and are connected by the circuit 69 to an audio frequency amplifier 102. and its attendant sound reproducer 103. This amplifier and reproducer may be in any of the conventional forms now known to the art consisting of cascade triode amplification, and

utilizing the various forms of reproducing units, horns, and cones.

The variations in the light affecting the photo-electric cell 58 cause an electronic emission from cathode to anode, and these elements being placed in a circuit with and attendant to the resistance 70, and battery source 71, setup a current flow va 'ng in frequency and potential corresponding to the light changes atfecting photo-electric cell 58.

The alternating pulsating component of this current flow passes throughthe condenser 72 to the grid 76 of a triode, and from the negative terminal of the battery source 71 to the filament 74: of the triode. Tliis filament is heated by the battery source regulated by the controlling resistance 75. The plate 77 of the triode is connected to the primary winding 78 and thence to the positive terminal of the battery source 7 9 the negative terminal of which is connected to the positive terminal of the filament battery source 80 in the conventional manner.

It'is apparent that interruptionsand variations caused by the striatic structure 44 to light falling on the photo cell 58 set up similar electrical variations in the primary winding 78 and like variations in the secondary winding 81. Secondary winding 81 controls the grid filament circuit of the triode amplifier consisting of the triode grid 98, filament 95. filament heating battery source 96. plate 99, primary winding of the step down transformer 100 and the plate supply battery 97.

The secondary of the transformer 100 is tuned by means of the condenser 101 in order that its outputbe peaked at a frequency approximately that of the control synchronizing frequency, after which it passes to the collector'rings 94 of the alternator 93 where it serves to control the speed of the alternator synchronous to that of the alternator incorporated in the recording mechanism.

The alternator being attached to and a part of the common shaft driven by the motor 92, the speed of this shaft and the drive pulley are synchronous to the motor 36, and drive pulley 35 of the recording mechanism illustrated in Figure 1.

Further speed regulation is obtainedby means of a mercury balance wheel 91 similar to balance wheel 37. As before stated uniform synchronous motion is one of the main objects of my invention, and I have described a method whereby such variations in speed of the record ng mechanism due to voltage variations in the supply current and other causes are neutralized at the translation or reproducing system, by the introduction of the same errors, and variations of speed, as those encountered during the period of recording. V

I have described a preferred embodiment of my invention. but it is clear that numerous changes could be made without departing from its spirit, and I do not wish to be limited to' the details before specified.

I claim 1. In systems for recording sound by electro-optical methods upon a light sensitive moving film the combination of: a sound modulated light arranged to light afiect said film; an alternator adapted to generate electrical impulses and arranged to rotate in common with a prime mover utilized to move said film, and a second light modulated by the impulses from said alternator and arranged to light affect said film simultaneously with said first mentioned light.

2. In an apparatus for recording and reproducing sound by electro-optical methods, the combination of a double striatic structured film representing speech frequency and synchronizing frequency records, a prime mover imparting motion to said film, an alternator rotating in connnon with said prime mover, photoelectric cells and attendant triode amplifiers for the interpretation of said film, producing energy similar in wave form and frequency to the original currents modulating the recording light devices, said energies being applied to loud speakers and said alternator for the production of true representation of the original sounds of speech frequency.

3. In apparatus for the recording and reproduction of sound by electro-optical methods, the combination of a film base carrying a double striatic structure representing on one structure speech frequency currents, and the other representing a synchronizin pulse, photoelectric and amplifier means ti producing energy similar in wave shape and form to the photographic representation of the original energies, means for combining the synchronizing energy with that of an alternator, rotating in common with a prime mover driving said film, in such a maimer as to produce a correction torque during certain phase relationships of said synchronizing energies.

4. A system for electro optically reproducing sound from a moving film having a sound track and a speed control track thereon embodying: a single source of light; means for reflecting light from said source from said sound track to produce a sound modulated electric circuit and means for passing light from said source through said speed control track to produce a frequency modulated circuit operable to control the speed of said film.

5. A system for electro-optically recording sound upon a moving light sensitive film comprising: film moving means; an alternator driven in common with said film moving means and adapted to generate electrical impulses whose frequency varies in accordance with the speed of said film moving means, and means for photographing said impulses upon said moving film.

6. In a system for reproducing sound by electro-optical methods, the combination of: a film having a sound track representing speech frequencies and a speed control track representing synchronizing frequency records; means for producing energy similar in form and frequency to said synchronizing frequency records, and means for applying said energy to an alternator driven in com- 5 mon with a film moving means to control the speed of said film.

In testimony whereof, I have signed my name to this specification this 24th day of August 1927. l0 EDMUND H. HANSEN. 

